Reliable automotive braking systems are extremely important in ensuring motor vehicle safety. As such, braking systems must be designed and manufactured to extremely exacting standards. Problems with such systems, as measured or detected primarily by warranty returns, are carefully monitored for signs of correctable defects or other abnormal wear patterns.
In the case of warranty returns, brake designers and manufacturers test brake rotors to detect defects. Two characteristics representing potential defects include linear run out and thickness variation. Linear run out is the deviation of the brake rotor from straight-line, circular rotation, and includes both inbound and outbound run out. Thickness variation is the variation in thickness of the brake rotor and can occur where the brake surface is not consistently perpendicular with respect to the axis of rotation. This translates into run out when the rotor, caliper, and brake pads generate an uneven disc wear that produces two thin-to-high spots. Linear run out can also be the result of, for example, a warped brake rotor.
These rotor characteristics, whether from wear, manufacturing defects, or design defects, can produce pulsations in the brake system when brakes are applied, and therefore will cause a shuddering sensation in a braking motor vehicle. If a cause of an anomaly can be determined, these abnormal characteristics can be prevented. Therefore a large number of warranty returns can be avoided and a large amount of money can be saved.
Currently, brake rotors are initially inspected on the vehicle with a dial indicator. Measurements of rotor position and thickness are taken manually at various points around the rotor. When more in-depth testing is required, brake designers and manufacturers perform precision analysis of brake rotors in a laboratory environment. To accomplish this detailed lab testing, the brake rotors must be removed from the motor vehicle and shipped to the manufacturer, when the owner of the motor vehicle makes the warranty return. The transporting and testing of brake rotors is therefore an expensive, time consuming process. Additionally, dismounting and transporting the brake rotors can introduce additional defects (e.g. damage during shipment or corrosion of the rotor) and may result in analysis not representative of the on-vehicle behavior (e.g. because of the absence of lug nut torque).
For this and other reasons, improvements are desirable.